OFFSET
1,2
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
N. Ailon and Z. Rudnick, Torsion points on curves and common divisors of a^k - 1 and b^k - 1, Acta Arith. 113 (2004), 31-38. Also arXiv:math/0202102 [math.NT], 2002.
EXAMPLE
gcd(2^1-1, 3^1-1) = gcd(1,2) = 1, so a(1) = 1.
gcd(2^2-1, 3^2-1) = gcd(3,8) = 1, so a(2) = 2.
gcd(2^4-1, 3^4-1) = gcd(15,80) = 5, so 4 is not in the sequence.
MAPLE
select(n -> igcd(2^n-1, 3^n-1)=1, [$1..1000]);
MATHEMATICA
Select[Range[200], GCD[2^# - 1, 3^# - 1] == 1 &] (* Vincenzo Librandi, May 01 2016 *)
PROG
(Magma) [n: n in [1..200] | Gcd(2^n-1, 3^n-1) eq 1]; // Vincenzo Librandi, May 01 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Oct 22 2015
STATUS
approved